ML19317D871
| ML19317D871 | |
| Person / Time | |
|---|---|
| Site: | Oconee  |
| Issue date: | 11/13/1974 |
| From: | DUKE POWER CO. |
| To: | |
| Shared Package | |
| ML19317D867 | List: |
| References | |
| RO-269-74-18, NUDOCS 7912100587 | |
| Download: ML19317D871 (2) | |
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DUKE PO'4ER COMPANY OCONEE UNIT 1 g
Report No.:
50-269/74-18 Report Date:
November 13, 1974 Occurrence Date:
October 30, 1974 Facility: Oconee Unit 1, Seneca, South Carolina Identification of Occurrence:
Reactor coolant pressure transmitters out of calibration Conditions Prior to Occurrence:
Unit in cold shutdown Description of Occurrence:
On October 30, 1974, reactor coolant pressure transmitters RC 3A-PT1, RC 3A-PT2, RC33-PT1, and RC 33-PT2, for Oconee Unit 1, were found to te out of calibration by &5.9, +5.25, +2.6, and +4.97 percent, respectively.
These pressure transnitters provide reactor coolant pressure infor=ation to the Reactor Protective System.
The full scale error teasured as a result of transmitter drift was:
Channel A RC 3A-PTl
+47.2 psi Channel B RC 3A-PT2
+42.0 psi Channel C RC 33-PTl
+20.8 psi Channel D RC 33-PT2
+39.7 psi All four pressure transmitters drifted in the positive direction and were within 3.3 percent of each other.
The transmitters were last calibrated on May 7, 1974 and were out of calibration in the negative direction at that time.
Analysis of Occurrence:
The Reactor Protective System high and low pressure trips are actuated by signals from the affected pressure transmitters.
The high pressure trip setpoint drifted in a conservative direction and would have produced a trip at an actual pressure of 2301.8 psi rather than 2349 psi, the high pressure trip setpoint.
The low pressure trip setpoint would have occurred at an actual pressure of 1758.8 psi based upon the setting of 1806 which had been set to allow instru=ent drift.
The protective system =aximum allowable setpoints, shown in Figure 2.3-1A in the Technical Specifications, would have the lower limit lowered to 1758.8 psi.
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The variable low pressure trip setpoints are based upon core outlet temperature, not pressure, and therefore can be extrapolated to intersect
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the low pressure trip setpoint resulting frem transmitter drif t at 1758.8 psi and 535 F.
In relation to the core protection safety li=its, Figure 2.1-LA, this point is to the left and above the safety limit, as required to =aintain a conservative margin to departure from nucleate boiling (DNB).
It is concluded that the health and safety of the public was not affected.
Corrective Action:
The pressure transmitters were recalibrated to the required specifications.
To prevent similar occurrences, a check of these transmitters will be performed on a monthly basis until a sequence of tests can be perfor=ed to determine the cause of the lastrument drift.
Identical transmitters, calibrated to the sa=e specifications, will be subjected to a si=ilar temperature environ =ent over a period of time to determine resulting instrument drift.
Failure Data:
The RPS pressure transsitters are Motorola Type 56PH, ID No. 1224-0301.
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